I have a funky PCI card with multiple serial ports on it that loaded fine with the standard serial driver from my standard kernel, until… the revision changed and now instead of using the tried and true 16550 UART, it’s got some sort of super specialized proprietary version of that chip. The manufacturer says it’s 100% backwards compatible with the 16550 / 16550A chips, and theirs just adds some more functionality for industrial processes or something… blah.